Abstract
A new imidazolium salt, 1,3-bis(2-diphenylphosphanylethyl)-3H-imidazol-1- ium chloride (2), for the phosphine/N-heterocyclic carbene-based pincer ligand, PCNHCP, and its palladium complexes were reported. The complex, [Pd-(PCNHCP)Cl]Cl (4), was prepared by the common route of silver carbene transfer reaction and a novel direct reaction between the ligand precursor, PCNHCP·HCl and PdCl2 without the need of a base. Metathesis reactions of 4 with AgBF4 in acetonitrile produced [Pd(PCNHCP)(CH3CN)](BF4)2 (5). The same reaction in the presence of excess pyridine gave [Pd(PC NHCP)(py)](BF4)2 (6). The X-ray structure determination on 4-6 revealed the chiral twisting of the central imidazole rings from the metal coordination plane. In solution, fast interconversion between left- and right-twisted forms occurs. The twisting reflects the weak π-accepting property of the central NHC in PCNHCP. The uneven extent of twisting among the three complexes further implies the low rotational barrier about the Pd-NHC bond. Related theoretical computations confirm the small rotational energy barrier about the Pd-NHC bond (ca. 4 kcal/mol). Catalytic applications of 4 and 5 have shown that the complexes are modest catalysts in Suzuki coupling. The complexes were active catalysts in Heck coupling reactions with the dicationic complex 5 being more effective than the monocationic complex 4.
| Original language | English |
|---|---|
| Pages (from-to) | 6822-6829 |
| Number of pages | 8 |
| Journal | Inorganic Chemistry |
| Volume | 43 |
| Issue number | 21 |
| DOIs | |
| Publication status | Published - 2004 Oct 18 |
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All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Inorganic Chemistry
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A new tridentate pincer phosphine/N-heterocyclic carbene ligand : Palladium complexes, their structures, and catalytic activities. / Lee, Hon Man; Zeng, Jing Yao; Hu, Ching-Han; Lee, Ming Tsung.
In: Inorganic Chemistry, Vol. 43, No. 21, 18.10.2004, p. 6822-6829.Research output: Contribution to journal › Article
TY - JOUR
T1 - A new tridentate pincer phosphine/N-heterocyclic carbene ligand
T2 - Palladium complexes, their structures, and catalytic activities
AU - Lee, Hon Man
AU - Zeng, Jing Yao
AU - Hu, Ching-Han
AU - Lee, Ming Tsung
PY - 2004/10/18
Y1 - 2004/10/18
N2 - A new imidazolium salt, 1,3-bis(2-diphenylphosphanylethyl)-3H-imidazol-1- ium chloride (2), for the phosphine/N-heterocyclic carbene-based pincer ligand, PCNHCP, and its palladium complexes were reported. The complex, [Pd-(PCNHCP)Cl]Cl (4), was prepared by the common route of silver carbene transfer reaction and a novel direct reaction between the ligand precursor, PCNHCP·HCl and PdCl2 without the need of a base. Metathesis reactions of 4 with AgBF4 in acetonitrile produced [Pd(PCNHCP)(CH3CN)](BF4)2 (5). The same reaction in the presence of excess pyridine gave [Pd(PC NHCP)(py)](BF4)2 (6). The X-ray structure determination on 4-6 revealed the chiral twisting of the central imidazole rings from the metal coordination plane. In solution, fast interconversion between left- and right-twisted forms occurs. The twisting reflects the weak π-accepting property of the central NHC in PCNHCP. The uneven extent of twisting among the three complexes further implies the low rotational barrier about the Pd-NHC bond. Related theoretical computations confirm the small rotational energy barrier about the Pd-NHC bond (ca. 4 kcal/mol). Catalytic applications of 4 and 5 have shown that the complexes are modest catalysts in Suzuki coupling. The complexes were active catalysts in Heck coupling reactions with the dicationic complex 5 being more effective than the monocationic complex 4.
AB - A new imidazolium salt, 1,3-bis(2-diphenylphosphanylethyl)-3H-imidazol-1- ium chloride (2), for the phosphine/N-heterocyclic carbene-based pincer ligand, PCNHCP, and its palladium complexes were reported. The complex, [Pd-(PCNHCP)Cl]Cl (4), was prepared by the common route of silver carbene transfer reaction and a novel direct reaction between the ligand precursor, PCNHCP·HCl and PdCl2 without the need of a base. Metathesis reactions of 4 with AgBF4 in acetonitrile produced [Pd(PCNHCP)(CH3CN)](BF4)2 (5). The same reaction in the presence of excess pyridine gave [Pd(PC NHCP)(py)](BF4)2 (6). The X-ray structure determination on 4-6 revealed the chiral twisting of the central imidazole rings from the metal coordination plane. In solution, fast interconversion between left- and right-twisted forms occurs. The twisting reflects the weak π-accepting property of the central NHC in PCNHCP. The uneven extent of twisting among the three complexes further implies the low rotational barrier about the Pd-NHC bond. Related theoretical computations confirm the small rotational energy barrier about the Pd-NHC bond (ca. 4 kcal/mol). Catalytic applications of 4 and 5 have shown that the complexes are modest catalysts in Suzuki coupling. The complexes were active catalysts in Heck coupling reactions with the dicationic complex 5 being more effective than the monocationic complex 4.
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U2 - 10.1021/ic049492x
DO - 10.1021/ic049492x
M3 - Article
C2 - 15476383
AN - SCOPUS:6344267173
VL - 43
SP - 6822
EP - 6829
JO - Inorganic Chemistry
JF - Inorganic Chemistry
SN - 0020-1669
IS - 21
ER -